You do know what a flywheel is, I hope. Aftermarket pulleys and flywheels serve somewhat of a same purpose: they're both meant to reduce the amount of power taken from the engine for all the drivetrain movements so that more power gets to your wheels. The way a flywheel upgrade does it is by reducing the weight by some 50% or so. It's then easier to spin the flywheel and it doesn't take as much power. The same is done with the underdrive pulleys: they're made smaller and fit smaller belts onto them so that it's easier to get everything moving. Unorthodox Racing is just a brand that makes the pulleys, they're most popular. Hope I helped you some.
(Edited by S13Grl at 8<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>6 pm on Oct. 30, 2001)